This invention relates to roller cone drill bits. More particularly, the invention relates to roller cone bits having an improved pressure compensating device therein.
Sealed bearing roller cone drill bits generally incorporate a compensating mechanism to limit the pressure differential between the lubricant sealed within the drill bit and the well bore fluid. The most common device is a flexible diaphragm separating the two fluids. The diaphragm responds to the conditions in the well to maintain a balanced pressure across the primary dynamic seals in the drill bit.
As previously mentioned, these devices also typically compensate for volumetric changes of the lubricant which occur in the form of leakage or through thermal expansion.
Previously constructed compensators have been generally successful in performing the desired functions. Bit manufacturers currently supply acceptable compensators. However, difficulty is encountered during assembly due to the relatively large number of separate components that must be carefully inserted in the correct sequence into each cavity in each arm of each drill bit. Most of the compensators utilize some form of rolling diaphragm that isolates the drilling mud from the bit lubricant. The rolling action of the diaphragm compensates for volumetric changes in the lubricant.
U.S. Pat. No. 4,276,946 issued Jun. 7, 1986 illustrates one previously constructed compensator that also utilizes the resiliency of the diaphragm to assist in determining when the proper quantity of lubricant has been injected into the system.
The purpose of the invention is to provide an improved pressure compensating assembly for use in sealed bearing roller cone drill bits to balance the pressure in the bit lubrication system and the drilling mud in the well adjacent to the drill bit. Also, the compensators serve to act as a reservoir to provide a limited amount of additional lubricant to the bit bearings if some lubricant is lost to the exterior of the system.
The inventive pressure compensator device is in the form of a cartridge assembly that is inserted as a unit into drill bits. This negates the necessity for assembling the compensator as it is placed into a cavity formed into the drill bit. Most often, a drill bit includes three cutter supporting arms and each arm is provided with a pressure compensating device. Thus, assembly time and cost saved by the inventive cartridge type compensator is multiplied by three for each drill bit.
In addition, the ability to preassemble the compensators provides better uniformity and substantially reduces problems in filling the lubricant reservoir to the correct volume.
The invention herein provides for a superior pressure compensating means as compared to the prior art. The cartridge type construction of the invention is easily installed and filled with the desired volume of lubricant, yet, the inventive compensator is effective in accommodating the volumetric changes in the lubricant as well as balancing the pressures in the lubricant with that of the well drilling fluid. In addition, the invention contemplates a novel means for retaining the compensator assembly in position in the drill bit.